A stop process of stopping an output from a fuel cell by stopping the supply of fuel gas and oxidation gas to the fuel cell when a required power generation amount for the fuel cell is smaller than a predetermined power generation amount, so-called an idle stop is known as a control of fuel gas.
In the case of operating the fuel cell again in an idle stop state, a time is required which is sufficient for a voltage to increase up to a required voltage after the start of an electrochemical reaction after the supply of the fuel gas and the oxidation gas is resumed. Thus, in the case of using the fuel cell as a vehicle drive source, required power cannot be immediately output even if an accelerator pedal is depressed during an idle stop. Such low responsiveness has caused a reduction in drivability. Accordingly, in JP4182732, fuel gas or oxidation gas is supplied at a predetermined timing during an idle stop to ensure responsiveness regardless of required power.
Even if the supply of the fuel gas and the oxidation gas is stopped, the fuel gas and the oxidation gas remaining in the fuel cell continue to chemically react due to permeation through an electrolyte membrane. If the fuel gas is consumed by the chemical reaction of the fuel gas and the oxidation gas having permeated, an anode internal pressure decreases and oxygen permeates through the electrolyte membrane during the idle stop to cross-leak to an anode side. As a result, a state occurs where oxygen is unevenly distributed in an anode (hereinafter, referred to as an uneven distribution of gas). If the uneven distribution increases, a hydrogen front is formed by the oxygen unevenly distributed in the anode when the operation of the fuel cell is resumed to supply the fuel gas and the oxidation gas, which results in the deterioration of an electrode catalyst. Specifically, carbon carrying platinum as the electrode catalyst reacts with water produced by an electrochemical reaction in a cathode, thereby being changed to carbon dioxide. The platinum carried on the carbon elutes to reduce a catalytic function.
To prevent such deterioration of the electrode catalyst by the hydrogen front, fuel gas is supplied when an uneven distribution of gas is detected during an idle stop in JP4432312. It should be noted that a pressure, density, electrode voltage or the like in the anode is detected by a sensor and the uneven distribution of gas is detected based on that detection value.